1. Field of the Invention
This invention relates to a helicopter whose rotors are equipped with flaps which regulate the rotor lifts during horizontal flight so as to suppress fuselage vibration and enable stable flight.
2. Description of the Prior Art
The vertical flight of a helicopter is stable since equal amounts of lift are produced by the rotors and flapping, dragging and the like therefore do not occur.
In horizontal flight, however, the leading rotor has a larger air speed than the trailing rotor and thus generates greater lift. The lift imbalance resulting from the different positions of the rotors relative to the fuselage gives rise to flapping and dragging which cause vibration of the fuselage.
This vibration, which is a problem peculiar to helicopters, has conventionally been relieved by the installation of a stabilizer. In the Bell UH-1H, for example, this stabilizer is called a "stabilizing bar" (see Jane's All the World's Aircraft 1984-85, p. 322, right column, line 12 from the bottom), while in the Hiller UH-12ET it is referred to as a "servo rotor" (op.cit. p. 418, left column, line 17 from the bottom). Such a stabilizing bar or servo rotor is a mechanism for adjusting the pitch angle of the rotor in response to changes in the helicopter attitude (namely, a feathering mechanism) and does not eliminate extraordinary rotor flapping and/or dragging. Therefore, such stabilizers have no essential effect toward suppressing fuselage vibration.